Lobe type pump adjustment

ABSTRACT

A gear mounting arrangement for lobe type air pumps. Angular adjustment between a gear (a form of hub) and its (lobe carrying) shaft permits a desired angular phase adjustment between the intermeshing lobes. The gear moves axially on its shaft and is held in place by positive screw or nut on one face and retained on the other face by a belleville spring. Rotation of the nut causes axial displacement of the gear and consequent phase adjustment.

This invention relates to adjustable gearing and displays particularutility in the art of lobe or rotor type pumps.

As illustrated in U.S. Pat. No. 2,444,773 to Gondek, a lobe-type pump isdefined by a chamber in which rotate two intermeshing lobe-type rotors.The intermeshing rotors carry two, three or any desired number of lobes,the rotors turning in opposite directions and being carried by parallelshafts. It is of paramount importance in such pumps that the (angular)phase between the rotors be accurately established and maintained so asto prevent abrasion between the lobe surfaces. One manner ofestablishing the desired phase, as described in the Gondek patent, is toemploy a spline connection between an auxiliary or driven gear and itsshaft. The auxiliary and driving gear may be helical gears. A nut andadjustable shims are provided on the shaft which carries the auxiliarygear. With this arrangement, axial movement of the auxiliary gear on itsshaft, by changing the shim thickness, will cause the desired phaseadjustment between the two lobed rotors. While apparently operable inthe manner intended, the Gondek apparatus displays the obviousdisadvantage of having to disassemble a portion of the apparatus inorder to carry out the phase adjustment.

Other methods of accomplishing similar phase adjustment are known, suchas shown by U.S. Pat. No. 2,304,770 to Nichols and U.S. Pat. No.2,660,115 to Ras. Again, while such prior art constructions haveapparently served the purpose intended by their originators, they suffersome disadvantage, such as relative complexity and number of partsrequired.

According to the practice of this invention, the angular phase betweenthe intermeshing rotors of a lobe-type pump may be adjusted by axialmovement of a gear relative to the shaft upon which it is mounted.However, in lieu of shims such as employed in the prior art, one or morebelleville springs is employed. The gear is held axially in place by abelleville spring which holds the gear against an adjusting nut. Bymerely turning the nut relative to its shaft, axial movement of the gearis realized. The gears having helical teeth, the desired phaseadjustment is effected. It is also possible to employ helical splinesand square gear teeth. With this latter arrangement, axial movement ofone of the meshing gears relative to its shaft also effects the desiredphase change or adjustment.

IN THE DRAWINGS:

FIG. 1 is a sectional view of a portion of a lobe type compressorillustrating the invention.

FIG. 2 is an enlarged view similar to a portion of FIG. 1.

FIG. 3 is a typical cross-section of a lobe type pump such as that ofFIG. 1.

FIG. 4 is a typical set of load-deflection curves for belleville typesprings and illustrates how an optimum spring is selected.

FIG. 5 is a load-deflection curve of a belleville spring when operatedalong its yield range.

Referring now to the drawings, the numeral 10 denotes generally a lobetype pump of conventional construction such as shown in U.S. Pat. No.2,444,773 to Gondek. The pump includes an outer casing 12 and endclosures 14 and 16. The numeral 18 denotes a bearing for input powershaft 22, the latter carrying lobes 24. A parallel, driven shaft 26carries lobes 28. Meshing gears 30 and 34 are coupled to the ends ofshafts 22 and 26. As shaft 22 is turned by a motor or other prime mover,gear 34 attached thereto as by splines 36 turns and meshes with gear 30,turning shaft 26 through splines. Lobes 24 and 28 (note FIG. 3) thusrotate in opposite directions and effect a pumping action in theconventional manner.

The numeral 38 denotes a belleville spring of conventional constructionand having its larger diameter in abutting contact with one face of gear30. A sleeve 40 may extend between lobe 28 and the narrow diameter ofthe belleville spring, the sleeve 40 surrounding shaft 26. Nut 24 isthreaded on the end of shaft 26.

In the illustrated form of the invention, the splines 36 are straight,while the gears 30 and 34 each carry meshing helical teeth. It will beunderstood, in view of the description which will follow, that thesplines 36 may be helical and the meshing teeth of gears 30 and 34straight or square.

The operation of the device is as follows. The apparatus is assembledwith the intermeshing lobes 24 and 28 positioned approximately in thedesired phase or angular relationship. The nut 42 is tightened againstthe force exerted by belleville spring 38 until gear .[.34.]. .Iadd.30.Iaddend.is placed in that axial position along shaft 26 which willyield the desired phase or angular relationship between the lobes 24 and28. Should the initially chosen phase or angular relationship betweenthe lobes change, as for example due to mechanical wear, it is onlynecessary to adjust the nut 42 so as to cause the auxiliary or drivengear .[.34.]. .Iadd.30 .Iaddend.to move axially along a shaft 26 untilthe desired phase relationship is again realized. In the illustratedembodiment, with splines 36 parallel to the axis of shaft 26, motion ofhelical gear .[.34.]. .Iadd.30 .Iaddend.axially along its shaft willcause rotation of gear .[.30.]. .Iadd.34 .Iaddend.with consequentangular adjustment of the rotor lobe carried by shaft 22. In the eventthat the splines 36 are pitched somewhat at an angle to the axis ofshaft 26, i.e., helical splines and spur gears are employed, axialadjustment of gear .[.34.]. .Iadd.30 .Iaddend.along the shaft 26 willcause slight rotation of gear .[.34.]. .Iadd.30.Iaddend., causing acorresponding rotation of gear .[.30.]. .Iadd.34 .Iaddend.and shaft 22which carries the other lobed rotor.

Referring now to FIG. 4 of the drawings, a set of typicalload-deflection curves is illustrated for belleville type springs. It isseen by the selection of the curve h/t=2.1 a fairly constant springforce is realized over a substantial range. The belleville spring mustexert sufficient force that gear .[.34.]. .Iadd.30 .Iaddend.is alwaysurged against the side of nut 42. That is to say, the axial force due tothe pumping must always be less than the spring force. The spring isalso selected to be strong enough to require that the nut be tightenedto its normal torque range, thus insuring that the nut will not back offor loosen. The axial position of the gear .[.34.]. .Iadd.30 .Iaddend.canbe adjusted over the optimum deflection range of the belleville spring38 without appreciable variation of torque on the nut 42, as indicatedby the double headed arrow of FIG. 1. As is well-known to workers inthis art, belleville springs can be employed in series or in parallel onany combination to obtain the required force and deflection range for aparticular application.

Operation of the belleville spring is possible in three generalconditions:

1. Optimum range (FIG. 4).

By selection of h/t=2.1 a fairly constant spring force is realized overa substantial range.

2. In a particular design, spring force for suitable spring size may betoo low to give proper nut locking force and/or gear clamping force;then a spring may be used in the linear portion of the curve shown inFIG. 4. Axial adjustment may then be employed with spring force varyingbetween acceptable limits. Springs may be used in series or parallel orcombinations of both to obtain required force-deflectioncharacteristics.

3. A belleville spring suitably tempered, can be deflected beyond itsyield point and in effect increase its deflection range, resulting inlower spring cost (see FIG. 5). A precaution must be made to carry outmajor adjustments in one direction only. A small reverse adjustment ispossible.

While illustrated as displaying particular utility in a lobe type pump,it will be apparent that the invention exhibits utility in anyapplication wherein angular phase between a hub and its shaft .Iadd.orbetween two shafts .Iaddend.must be adjusted.

In one example employing the invention, the pump 10 was employed as anair pump and the helix angle of gears 30 and 34 was 19.005°. The outsidegear diameter was about 41/2 inches. The axial adjustment range of gear.[.34.]. .Iadd.30 .Iaddend.was 0.076 inches which allowed a gear toothto spline tolerance of plus and minus 5 minutes and spline center lineto rotor center line of plus and minus 5 minutes. The maximum forceexerted by the belleville spring 38 was 9,000 pounds. A tolerance ofplus and minus 8 minutes or indexing of gears and plus and minus 5minutes on rotor center line to spline center line results in a requiredaxial range of the helical gear .[.34.]. .Iadd.30 .Iaddend.ofapproximately 0.099 inches. In another example, the belleville spring.[.34.]. .Iadd.38 .Iaddend.was operated in the range shown at FIG. 5.The desired phase between the lobes was fixed when the nut 42 exertedabout 6,000 pounds force against the spring. For all subsequent phaseadjustments, the nut was turned to further compress the bellevillespring up to about 9,000 pounds force. The range was thus in the yieldpoint range of the spring metal, as indicated by the lagging return(hysteresis) path.

The phase adjustment has been shown with respect to the driven gear 30.However, it could also be made on the driving gear 34.

I claim: .[.1. A connection between a shaft and a hub for varying theangular phase relation therebetween, said shaft and hub having at leastone interengaging spline, an abutment adjustably positioned along saidshaft, said abutment contacting one face of said hub, a biasing springcontacting the other face of said hub, said spring being compressed,whereby a spring force urges the hub against the abutment..]. .[.2. Theconnection of claim 1 wherein said spline is at an angle to the axis ofsaid shaft, whereby axial adjustment of said abutment along the shaftcauses the hub to rotate relative to the shaft..]. .[.3. The connectionof claim 2 wherein said abutment is defined by a nut threaded on saidshaft..]. .[.4. The connection of claim 2 wherein said spring is abelleville spring..]. .[.5. The connection of claim 4 wherein thelargest diameter of said bellevile spring contacts one face of the hub,and wherein a collar is axially fixed relative to said shaft, and thesmallest diameter of said belleville spring contacts and abuts one endof said collar..]. .[.6. The connection of claim 1 wherein said hub is agear, and including a second gear secured to a second shaft, said secondgear meshing with said first-mentioned gear, said first and second gearshaving helical teeth, whereby axial movement of the first gear on itsshaft rotates the second gear and its shaft..]. .[.7. The connection ofclaim 6 wherein said first and second shafts each carry a plurality ofelongated, meshing lobes, whereby adjustment of the abutment along thefirst-mentioned shaft causes angular phase adjustment between thelobes..]. .[.8. The connection of claim 1 wherein said hub carrieshelical gear teeth on its outer periphery..]. .Iadd.9. A connectionbetween a shaft and a hub, said shaft and hub having at least oneinterengaging spline, an abutment adjustably positioned along saidshaft, said abutment contacting one face of said hub, a biasing springcontacting the other face of said hub, said spring being compressed,whereby a spring force urges the hub against the abutment, said splinebeing at an angle to the axis of said shaft, whereby axial adjustment ofsaid abutment along the shaft causes the hub to rotate relative to theshaft. .Iaddend. .Iadd.10. The connection of claim 9 wherein saidabutment is defined by a nut threaded on said shaft. .Iaddend. .Iadd.11.The connection of claim 9 wherein said spring is a belleville spring..Iaddend. .Iadd.12. The connection of claim 11 wherein the largestdiameter of said belleville spring contacts one face of the hub, andwherein a collar is axially fixed relative to said shaft, and thesmallest diameter of said belleville spring contacts and abuts one endof said collar. .Iaddend. .Iadd.13. A connection between a shaft and ahub, said shaft and hub having at least one interengaging spline, anabutment adjustably positioned along said shaft, said abutmentcontacting one face of said hub, a biasing spring contacting the otherface of said hub, said spring being compressed, said hub carryinghelical gear teeth on its outer periphery, whereby a spring force urgesthe hub against the abutment. .Iaddend. .Iadd.14. The combination of twoshafts interconnected for rotation in unison by drive elements, thestructural relationship of said drive elements to one another and saidshafts being one wherein each of said drive elements is non-rotatablysecured to a respective one of said shafts and wherein axial movement ofone of the drive elements on its shaft effects a change in angular phaserelationship between said shafts, the improvement comprising, anadjustable abutment urging one of the drive elements axially along itsone shaft, a spring element maintaining the drive element in contactwith the abutment. .Iaddend. .Iadd.15. The combination of claim 14wherein said one drive element is secured to its respective shaft by aspline connection, the spline being at an angle to the said shaft,whereby axial movement of the one drive element relative to itsrespective shaft causes the one drive element to rotate relative to itsrespective shaft. .Iaddend. .Iadd.16. The combination of claim 14wherein said two drive elements are gears having meshing, helical teeth,whereby when said one drive element is axially moved along itsrespective shaft the other drive element is caused to rotate. .Iaddend..Iadd.17. The combination of claim 14 wherein said abutment is definedby a nut threaded on said shaft. .Iaddend. .Iadd.18. The combination ofclaim 14 wherein said spring is a belleville spring. .Iaddend. .Iadd.19.The combination of claim 18 wherein the largest diameter of saidbelleville spring contacts one face of the hub, and wherein a collar isaxially fixed relative to said shaft, and the smallest diameter of saidbelleville spring contacts and abuts one end of said collar. .Iaddend..Iadd.20. The combination of claim 14 wherein said first and secondshafts each carry a plurality of elongated, meshing lobes, wherebyadjustment of the abutment along the first-mentioned shaft causesangular phase adjustment between the lobes. .Iaddend.